【作者】 王斌华；

【导师】 吕彭民；

【作者基本信息】 长安大学 ， 机械设计及理论， 2009， 博士

【摘要】 混凝土泵车的臂架姿态复杂多变使泵车工况复杂，结构设计的轻量化要求以及机动灵活的使用要求使泵车结构复杂。泵车泵送工作中，车体振动导致臂架振动较大，且臂架动应力分布随臂架姿态的调节而变化。基于以上原因，对混凝土泵车的结构强度研究，尤其是臂架部分的动力学研究，有很好的应用价值。本文采用流固耦合理论和有限单元理论，对泵车关键结构——臂架进行动力学仿真分析，并结合现场动态测试试验和臂架母材焊接接头疲劳试验，展开臂架结构疲劳强度的研究。（1）针对混凝土泵车的工作原理和结构特点，结合现有输液管流固耦合理论的研究成果，提出基础有平动位移的悬臂输液管理论模型，并通过多体运动学理论和Hamilton变分原理，建立该模型的运动微分方程。考虑泵车臂架系统的多节臂和变截面的特点，采用有限单元理论建立臂架系统的流固耦合运动微分方程。（2）通过分析确定了臂架水平旋转至垂直于不同侧的前支腿和后支腿支撑点连线时为混凝土泵车的不利工况，并以此作为测试工况进行现场试验。根据全车有限元静强度分析和模态分析结果，选取其中应力较大的部位和动态薄弱部位作为测点位置，测试应力／应变历程。通过前支腿支撑油缸活塞杆应变历程测试数据，分析计算出转台垂向振动振幅响应、速度响应和加速度响应，作为臂架振动仿真分析的外部激扰，为仿真分析提供计算边界条件。在MTS（MechanicalTesting&Simulation）疲劳试验机上对泵车母材焊接接头试样进行应力比r=0．2的拉伸试验，获得不同应力水平时，焊接接头的循环次数，从而得到焊接试样疲劳极限σ_0.2=205MPa，并绘制Goodman疲劳极限线图用于疲劳强度评估。（3）选取混凝土流速U=2．265m／s和U=0m／s对比仿真分析，发现臂架振动响应均值相同，但稳态时两者振动幅值比值A₍U=0/A_U=2.265最大接近2，而改变Rayleigh阻尼系数则对臂架振动响应影响不大，说明混凝土的流动增加臂架振动阻尼效应显著。结合Matlab仿真分析与Ansys臂架三维有限元模型，对比测点应力测试结果与仿真计算结果，两者应力历程变化趋势相似，用Goodman疲劳极限线图评估，发现两者应力均值和应力幅值较接近，验证了仿真模型的合理性。对比臂架动荷系数法和流固耦合动态仿真计算结果，总体应力分布规律基本相同，但最大应力值有一定差异，且发生位置也不尽相同，说明考虑流固耦合的动力学仿真与实际情况更加接近，其仿真结果更能真实反映应力发生位置和应力值。（4）建立含倾角参数α的臂架流固耦合动力学方程，计算α=0°、20°、52°和80°时，臂架结构动应力历程，分析发现在臂架连接端焊缝位置易出现大应力集中现象，且随着臂架姿态的调整，应力值和发生位置均有改变。将各姿态下各节臂架的大应力点绘制于Goodman疲劳极限线图内，发现该泵车臂架在局部加筋位置疲劳强度不足，大应力发生位置较多位于箱梁内部，无法检测和维修，因此在设计阶段应对大应力点进行结构改进。（5）对疲劳强度不足的结构位置进行加强，并对加强后结构重新进行疲劳强度评估，分析结果说明加强方案可行，能满足疲劳强度要求。以上研究注重解决工程问题，研究方法和结论基于试验进行，分析方法可用于同类型产品的设计研发和强度校核。更多还原

【Abstract】 Attitude change of pump truck arms leads to the complicated working conditions.Design requirements of light-weight and maneuverability make arm structure complicated.Truck body vibration results in big vibration response of arms.Stress distribution on arms isvariable as arms attitude changs.So,it is necessary to carry out study on structure strength ofpump truck,especially on dynamics of arms.The arms,which are the key part of pump truck,are studied based on the fluid-solid theory and finite element theory.And the research onfatigue strength of arms is performed by the method of combining field test on pump truckwith experimentation on the fatigue resistance of the base material welded joints.（1）The horizontally moving fluid-tube cantilever model is put forward incorporating thestructural features of pump truck and the research achievements on cantilever pipe conveyingfluid.Dynamic differential equation of the model is derived based on kinematical theory andHamilton variation principle.（2）The most dangerous working situation where arm direction is perpendicular tosupporting point diagonal is concluded by mechanical analysis.So the field test is conductedunder this situation.According to the results of the finite element calculation and modalanalysis on whole model,the locations of high stress and weak in lateral stiffness are selectedas measuring points.The vertical amplitude response,vertical velocity response and verticalacceleration response of revolving table,which are used as boundary conditions of simulationanalysis,are concluded based on the analysis of measuring date of cylinder piston rod at thefront support.In the test conditions of stress ratio R=0.2,tensile fatigue tests on basematerial welded joints are carried out using MTS fatigue testing machine.The tests show thatthe fatigue limit of welded joints is 205N/mm².Based on Goodman equation,the GoodmanFatigue Limit Diagram of base material welded joints is plotted.（3）By contrast calculation with two concrete fluid flow velocities of 0rn/s and 2.265rn/s,the mean value of vibration response of arms are identical and the maximum amplituderatio(A_U=0/AU=2.265is approximate to 2.And by contrast calculation with the two Rayleigh damping ratio of 0 and 0.00845,the amplitude ratio is approximate to 1.So it is concludedthat the concrete fluid flowing can enhance the structural damping significantly.Compared thesimulation results which are carried out by MATLAB and ANSYS with the measuring results,the similar change tendency of dynamic stress history is verified.And the simulation resultsof mean stress and stress amplitude are close to that in measuring results according toassessment analysis in Goodman Fatigue Limit Diagram.Compared the results carried out bythe dynamic load coefficient method and our method,the stress distribution law is basicallysimilar,but the high stress value and the high stress location are not the same.Thecomparison result shows the availability of our method.（4）Dynamic differential equation of the arm system containing parameter of dip angleαis derived.According to the simulation results of arm system with parameters of dip angleas follows:α=0°,α=20°,α=52°andα=80°,stress histories are obtained.Not only doeshigh stress concentration always occur in weld position located in end of arms,but stressvalue and position also change with parameterα.The problems of insufficient fatiguestrength take place in ribbed plates according to assessment analysis in Goodman FatigueLimit Diagram.So,it is necessary to strengthen structure in design stage because of ribbedplates beside in box beams unable to repair for finished product.（5）Reinforcement schemes are designed and the fatigue assessment analysis onreinforced structure is performed again.The result shows that the method used is feasible.The study in this dissertation pays much attention to solve practical engineering problem.Conclusions are made on bases of experimental data.Analysis methods provide goodreferences for design and strength assessment of this kind of structure.更多还原